can't find my notes on this right now.
but i presume if you do this function as is and then in the matrix:
1. set (2, 2) to 1.0f
2. set (3, 2) to 0.0f

then it should be a clip plane-less matrix

not 100% sure right now, so let's merge as is, and consider adding a separate constructor without clip planes later.

ideally use ::getClippedProjectionMatrix() in general when you want a projection matrix with clip planes
(in the case that you have set them, it'll use them, else it'll return a matrix with these planes set)